1. Field of the Invention
This invention relates to the field of radio telephones, typically cordless telephones and, more particularly, to method and apparatus for storing a dial signal as telephone number information.
2. Description of the Prior Art
As is well known in the art, radio telephones are comprised of a radio telephone set having a handset and a base unit connected to wired telephone lines for exchanging speech signals between the wired telephone lines and the radio telephone set through a radio channel. The base unit and the radio telephone set are respectively provided with a pair of corresponding transmitters and receivers.
When a call signal arrives at a wired telephone line, the base unit transmits a paging signal to the radio telephone set through a predetermined control channel to form a speech channel. The paging signal includes a channel signal indicating one of a plurality-of speech channels. Then, the radio telephone set starts an operation to send out a paging response signal through the control channel in response to the received paging signal. The base unit detects the intensity of the received paging response signal sent out from the radio telephone set, i.e., the intensity of the paging response signal at the control channel. Then, the base unit stops the transmission of the paging signal when the detected intensity exceeds a predetermined level and switches the radio channel between the base unit and the radio telephone set from the control channel to the speech channel indicated in the paging signal. The radio telephone set also switches the radio channel from the control channel to a speech channel by the received paging signal. Thereafter, the base unit transmits a bell ringing signal to the radio telephone set via the speech channel. After transmitting a bell ringing signal, the base unit establishes a speech path between the wired telephone line and the radio telephone set when it receives an "off-hook" signal from the radio telephone set.
When the base unit receives a call origination signal (an "off-hook" signal) from the radio telephone set through the control channel while it is in a waiting state, it determines the request from the radio telephone set to originate a call and transmits a response signal which includes a channel signal indicating one of the plurality of speech channels. Then, the base unit establishes a speech path between the wired telephone line and itself, and switches the radio channel from the control channel to the speech channel indicated in the response signal. After receiving the response signal, the radio telephone set also switches the radio channel from the control channel to the speech channel in response to the received response signal. If the radio telephone set transmits a dial signal to the base unit through the speech channel, the dial signal is transmitted to the wired telephone line via the base unit.
Thus, the radio telephone apparatus is capable of receiving incoming telephone calls from the wired telephone lines and originating calls from the radio telephone set.
In the above described radio telephones, the telephone set is powered by a small storage battery to enable the telephone set to be carried easily. As a result, a RAM, which is used to store a plurality of telephone numbers to thereby reduce dialing operations, cannot be provided in the radio telephone set because the lifetime of the battery decreases if the voltage from the battery is continuously supplied to the RAM to store the telephone number information. The RAM is provided in the base unit because the base unit is powered by a D.C. power source converted from an AC power source.
In the prior art radio telephones, the storing of telephone number information is carried out as follows. First, a user picks up the handset of the radio telephone set to depress a registration key and a dial key (FIGS. 1 and 2). When the handset is picked up, the radio telephone set determines an "off-hook" condition and transmits a call origination signal to the base unit. Thereafter, the operation of call origination is carried out as described above. When the registration key is depressed after the speech channel between the base unit and the radio telephone set is established, a corresponding key signal is transmitted to the base unit. The base unit then waits for the dial signal transmitted by the radio telephone set in response to the received key signal. When the dial key is depressed after depressing the registration key, the dial signal corresponding to the depressed dial key is transmitted to the base unit and stored in the memory in the base unit. When the handset is placed down in its initial position after the dial key is depressed, an end signal is transmitted to the base unit. Therefore, the end operation is carried out and the radio telephone apparatus is returned to its waiting state again.
However, in prior art radio telephones, the telephone is in a busy state while the dial signal is stored in the memory as telephone number information because the base unit is connected to the wired telephone line electrically until the base unit receives the end signal in response to the handset being set down in its initial position i.e., hung up or placed "on the hook." As a result, an incoming telephone call from the wired telephone line cannot be received while the dial signal is being stored as telephone number information, therefore, the radio telephone apparatus cannot respond to an incoming telephone call.
The problem can cause significant inconvenience in a system capable of storing a large number of telephone numbers. For example, if 100 numbers are to be stored, the telephone apparatus will be in its busy state for a long time and many telephone calls will be missed.